This invention relates to a signal transmission apparatus for a steering operation board adapted to transmit signals between a control unit on the vehicle body and the steering operation board in the vicinity of a steering wheel, and more particularly to a signal transmission apparatus for a steering operation board which includes an acoustic-electric converter such as a microphone on the steering operation board.
In vehicles, since a steering wheel is positioned nearest to the driver, particularly to his hands, an operation board equipped with a variety of keys, switches or the like adapted to control and command road-vehicle apparatus and units is preferably mounted at the central portion of the steering wheel for the purpose of improving operability.
However, a steering mechanism adapted to transmit a rotational movement of the wheel to a steering shaft is complicated, so that it is difficult to wire signal cables for connecting the operation board mounted at the center of the steering wheel (i.e, steering operation board) to a stationary control unit. To facilitate such wiring work, pipes for wiring and/or slip rings for connection must be additionally mounted to the steering mechanism and arranged in a manner without intervening operation thereof. Further, a mounting space allocated to the steering mechanism is limited practically, such wiring work will encounter much difficulty.
In view of the above, the applicant of this patent application has previously proposed in improved system (U.S. patent application Ser. No. 399,582 filed on July 19, 1982) wherein the operation board is connected to the stationary control unit using slip rings and brushes, thereby to transmit electric power and signals through such connection lines. With this, it is possible to supply the operation board with source power and to transmit much information generated therefrom without a need of using numerous lines.
In such system, however, it is difficult to ensure satisfactory reliability for a long term by reason of using mechanical elements such as a slip ring and brush. For example, if the contact surface between the slip ring and the brush is oxidized or a pressing force exerted on the contact portions is lowered with the lapse of time, the circuit may be disconnected temporarily due to mechanical vibrations or so travelled from the outside. Transmission of electric power can be prevented from suffering an influence due to disconnection of the power supply circuit by, for example, employing a capacitor of relatively large capacity. As to transmission of signals, however, there is a fear of danger such that the received information includes an error and the stationary control unit may be malfunctioned.
In order to eliminate such adverse influence, a system utilizing light beams for transmission of signals has been also proposed. But in this system, since the relative position between an optical element (e.g., light emitting element) on the steering wheel and another optical element (e.g., light receiving element) on the stationary vehicle body side is changed upon rotation of the steering wheel at the time of steering, transmission of signals is interrupted temporarily.
To avoid such inconvenience, there has been further proposed an improved system wherein a number of light emitting elements are disposed annularly at the central portion of the steering wheel and a single light receiving element is disposed in a position facing them, so that a light beam from any one of those light emitting elements may always reach the light receiving element. However, in case the operation board is arranged on the steering wheel in a floating relation in this system, by reason of spokes for supporting the steering wheel being positioned between the light emitting and receiving elements, an optical path between both elements is interrupted by the spokes upon rotation of the steering wheel. Also, because a number of light emitting elements are required, such system is disadvantageous and not suitable for practical use in terms of cost and power consumption.
When a radio communication apparatus is equipped on the vehicle, the apparatus is necessarily disposed in a position fairly spaced from a speaking person, e.g., the driver. To prevent transmission of external noises, therefore, it is usually arranged that a mouthpiece such as a microphone is made separatable from the communication apparatus body, the mouthpiece is connected to the apparatus body through a cord, and when communicating, the mouthpiece is taken off the apparatus body to come near the mouth of the speaking person. But, when the driver attempts to talk, he must have the mouthpiece such as a microphone by one hand, so that the driver has to drive the car by the remaining one hand in such occasion, resulting in a fear of danger. Since the driver has the most frequent opportunity to make communication, it is preferable to make it possible for the driver to make communication safely.